1. Field of the Invention
This invention is related to fluid control valves and more specifically the corrosion resistant and heated valve apparatus and methods.
2. State of the Prior Art
Valves are used in myriad applications in which corrosive gases or liquids of various kinds have to flow through them. In some applications, for example, in some chemical vapor deposition (CVD) systems, certain valves have to handle both materials that are themselves corrosive and others that tend to react with each other and/or that may tend to condense or otherwise deposit in the valves and other piping and system components.
To avoid or at least minimize such unwanted condensation and/or deposition, the valves, piping, and other components are often made with stainless steel or other corrosion resistant materials and are heated in order to maintain their temperatures high enough to vaporize any materials that start to condense on their surfaces or to prevent reactions that, at lower temperatures, may form byproducts which would deposit on the surfaces. Pipe components are relatively easy to heat and maintain above such unwanted condensation or other reaction temperatures because of their relatively uniform shapes and dimensions, but valves are more difficult to heat uniformly. Even with electric heater jackets or blankets surrounding their exterior surfaces, “cold spots” are common at some exterior and interior surfaces where contact with the heater jacket is not direct. “Cold spot” in this context means a spot or location on or in a valve or other component where the temperature cannot be maintained at a desired heated level during operation.